The Greenland melt

Last July (2012), I heard from a colleagues working at the edge of the Greenland ice sheet, and from another colleague working up at the Summit. Both were independently writing to report the exceptional conditions they were witnessing. The first was that the bridge over the Watson river by the town of Kangerlussuaq, on the west coast of Greenland, was being breached by the high volumes of meltwater coming down from the ice sheet. The second was that there was a new melt layer forming at the highest point of the ice sheet, where it very rarely melts.

A front loader being swept off a bridge into the Watson River, Kangerlussuaq, Greenland, in July 2012. Fortunately, nobody was in it at the time. Photo: K. Choquette

I’ve been remiss in not writing about these observations until now. I’m prompted to do so by the publication in Nature today (January 23, 2013) of another new finding about Greenland melt. This paper isn’t about the modern climate, but about the climate of the last interglacial period. It has relevance to the modern situation though, a point to which I’ll return at the end of this post.

The big news is that this group has managed to obtain and use the information in ice from the Eemian — the peak of the last interglacial period, about 125,000 years ago — in Greenland. Getting usable Eemian ice from Greenland has been a Holy Grail of ice core research for the better part of two decades. We thought, back in the early 1990s, that we had obtained Eemian ice in the GISP2 and GRIP ice cores drilled near the ice sheet summit. It turned out that the lowermost part — anything older than 100,000 years — was messed up by ice flow, making it impossible to learn anything much about climate from it. The Danish group then led a project further to the north at “North GRIP” that, based on radar-echo-sounding data, should have had an intact Eemian period. But the temperature at the base at NGRIP was higher than expected, and the Eemian ice had melted away.

The latest attempt was the “North Eemian” (NEEM) site in northeast Greenland. Here too, the initial results were disappointing. As at GISP2 and GRIP, there are folds in the ice, and some of the layers containing the ice of Eemian age are repeated several times. However, in this case the folds are very large, and there are continuous sections that are not scrambled; they are just a bit out of order. It took significant work, but the group has unfolded the data from the folded layers and it is now evident that the goal of the NEEM project– having an interpretable section of Eemian ice — has succeeded after all.

The findings are spectacular. In the Eemian ice, there is clear evidence of significant melting of what would then have been snow at the surface. The amount of air trapped in the ice undergoes rapid fluctuations, resulting from the fact that ice that melts and then refreezes generally winds up with fewer air bubbles in it than the original porous snow. There are also strong fluctuations observed in soluble gases such as N2O whereas variations in the oxygen isotope concentration — both in the molecular oxygen (O2) in the air and in the ice (H2O) itself — are small. The isotope concentration of the O2 can be matched to that in undisturbed ice from the same time period in ice cores from Antarctica, providing a way to date the ice, showing unambiguously that non-disturbed layers are preserved from the peak of the Eemian period, about 125,000 years ago.

Qualitatively, the evidence for melt in the NEEM Eemian ice shows that it was warm at the time. Obviously. But more interestingly, the last year of the NEEM project was 2012, and researchers were able to witness first hand what the formation of melt layers mean at NEEM in terms of the ambient conditions. In July 2012, the NEEM saw above-freezing temperatures for six consecutive days (10 to 15 July), with rain events on 11 and 13 July. When the water refroze, it formed several distinct, clear layers of ice (which we call a “melt layers”) between 5 and about 60 cm down in the snow, about 1 cm thick. This is a rare event. It was so warm over Greenland in that week that a significant melt layer also formed up at the Summit; in fact, the entire surface of the ice sheet was melting.

That hasn’t happened — not once — in the entire satellite record (see Jason Box’s excellent blog, meltfactor.org for more on this, and Marco Tedesco's paper.). In fact, examination of melt layer records from ice cores at Summit shows that a melt layer like the one that formed in 2012 was the most significant Greenland melt event since at least the late 19th century. If you drill about 100 m down into the ice and recover an ice core, you invariably find that layer, shown in the photo below (the bright line at which the person’s thumb is pointing)..Greenland ice core from ~80 m depth. E. Steig photo.

According to a recent paper on the 2012 melt by Nghiem et al., in Geophysical Research Letters, the 19th century event dates to 1889. One has to go back about 700 years to find the next such event, and overall, these are about once-in-250 year events over the last 4000 years. Prior to that, they occur more frequently — about once per century during the mid Holocene “climatic optimum”, when it was on average much warmer than present in Greenland in summer, due to the peak in Northern Hemisphere insolation due to changes in the earth’s orbit (Milankovitch forcing). Even during the mid-Holocene, though, there is no evidence from the ice cores that there was sufficient melting to create such strong anomalies in the air content and trace gas concentrations in the ice, as was observed in the Eemian in the NEEM ice. Thus, it was even warmer during Eemian than during the mid Holocene.

How much warmer was it? Jason Box estimates from satellite data that the temperature in July 2012 at high elevations over the Greenland ice sheet was a full 10°C (18°F) warmer than the daily average of the 2000′s decade; 1 standard deviation is about 3°C, so this is about a 3-sigma event. If, as the NEEM researchers estimate, the same sort of temperatures were required to produce the EEM melt layers, it suggests that during the EEM in Greenland it was also about 10°C warmer than present in the summer — but not just once per century, but much more often, perhaps every summer. I’m interpreting a bit here: the NEEM group doesn’t actually use the presence of melt layers per se to estimate the summer temperature; rather, they use the observation that the δ18O values of the ice at this time are >>-33 ‰. δ18O is a proxy for temperature in Greenland ice, and the NEEM paper uses this to estimate that the temperature must have been about 8°C (+/-4°C) warmer than present. Not coincidentally, the δ18O values of the snow and rain that fell in July 2012 was also >-33 ‰.

None of this should be interpreted to suggest that we are in “Eemian-like” conditions just yet. After all, there has only been one Eemian-like melt event observed in modern times, and the extremely warm summer of 2012 clearly involved anomalous weather conditions — a particular pattern of pressure anomalies over the northern high latitudes (Marco Tedesco's paper) that may also partly account for the exceptional low sea ice cover that year. The 2012 event, however, gives us a flavor of what the future is likely to bring. It will be very interesting to watch the satellite imagery over Greenland in the next decade and beyond.

What are the implications for the Greenland ice sheet? Possibly, that it is less sensitive to climate warming than some of the higher-end estimates suggest (e.g. Cuffey and Marshall (2000) suggested Greenland could have contributed > ~4 m to EEM sea level), though very much in line with more recent estimates (e.g. Pfeffer et al. (2008)). The estimated temperature change of ~8°C is quite a bit warmer than most previous estimates which are more in the range of 2-5°C (though the uncertainty estimates clearly overlap). Thus, whatever the contribution of mass loss from the Greenland ice sheet to the huge (4-8 m) rise in sea level of the Eemian, it occurred under very strong temperature forcing.

The presence of Eemian ice at the NEEM site itself places constraints on the ice sheet configuration. It obviously rules out any configuration in which this area of the Greenland ice sheet was gone. That typically occurs in ice-sheet model simulations that involve more than about 2 m of sea-level-equivalent mass loss. Thus, the NEEM ice core record suggests both that temperatures may have been warmer than once thought, and and that the ice sheet mass loss was unlikely to have been >2 m of sea level.

The new data from the NEEM ice core may also point to a lower limit on the magnitude of the Eemian sea level contribution from Greenland. Evidently, it can become very warm indeed over Greenland — much warmer than most previous modeling exercises have considered. Combined climate/ice sheet model estimates in which the Greenland surface temperature was as high during the Eemian as indicated by the NEEM ice core record suggest that loss of less than about 1 m sea level equivalent is very unlikely (e.g. Robinson et al. (2011).

There are caveats of course — the new data is just from one site, and estimates of the total ice loss don’t provide information about the rate at which that loss occurred. Still the new data show that Greenland, while evidently contributing significantly to Eemian sea level, cannot have contributed more than half the total — despite the strong forcing. This once again points to Antarctica as the major source of Eemian sea level rise. There are only about 3 m of sea level rise available from West Antarctica, and it remains unclear whether all of West Antarctica may have collapsed. On that subject, look for some more exciting ice core news in the near future, from a core at Roosevelt Island by a New Zealand led team.

Perhaps they were working on the bridge and went too long. Then they realized the bridge was too weak to support the machine to try to escape. They would park in the safest position and run for it before the bridge collapsed.

[Response: Well, now we’re both speculating about what “really” happened. Back to the climate aspect: this bridge was built in the late 1950s, so this was unequivocally the maximum flow it had had to deal with.–eric]

Found this video, looks like there had been some collapse (undermining?) of the bridge, involving the loader, prior to its abandonment. Looking at the berm, yeah, you have to wonder what that was supposed to accomplish. http://www.youtube.com/watch?v=WrIX-WzWA8k

Eric, you say ‘…A key difference is that CO2 was not as high as today, but insolation forcing was much higher.’

I imagine that the ‘bad’ side of that observation is that our present higher CO2 means the surface temperatures will persist higher over night, while an insolation forcing has most of it’s effect only when the sun is shining.

So today’s higher CO2 is a gift that keeps on giving energy to the icecap 24/7, while insolation via orbital variations is mitigated partly by the day/night effect.

I don’t understand how one forcing is different than another. Why is the energy from CO2 different from a change in albedo. Is that standard metric of W/m2 an insufficient description of the processes?

Jeffrey,
I’ll take a stab, although I’m sure there are others who could do better.

A lot has to do with the distribution of the forcing. For instance, Eric refers to the 40 W/m^2 of insolation forcing during the Eemian in comparison to 2 W/m^2 due to current CO2 (and equivalent?) loading. The first number actually comes from the forcing as measured at 65 degrees latitude; globally averaged, it is zero. (The earth still casts the same size shadow; but the higher tilt exposes north and south extremes to more direct sunlight.) So, you only get regional effects directly. Now, if those regional effects cause other changes, such as a change in albedo (ice melts), then you can get global effects indirectly.

In addition to spatial distribution, there is distribution over time. Polar winters are continuously dark; there is no positive forcing in the winter, and albedo counts for little.

Also, the albedo state of the surface matters. Ice would reflect most of the 40-watt solar forcing, but when it melted, water would absorb most of it. I suppose when the earth was in a snowball state, orbital variations had little effect because a) most of the surface had a similar, high albedo, b) whatever effect they did have was not enough to raise the temperature of the ice enough to start melting. I guess this goes back to ‘feedbacks are everything.’ If high seasonal insolation occurs when ice is near a melting point, it can have a much larger effect than when it doesn’t.

At a finer grain, you also have different absorption spectra for different surface materials. So, a given amount of energy in the solar wavelength band may or may not have the same effect as the same amount of energy in the IR band. There is a spectral graph here: http://frienergi.alternativkanalen.com/Water_Atoms.htm

So, no, this measurement is fine for the broad strokes, but it is not enough to paint the whole picture.

I am thinking that regardless of these results sea levels are rising and EAIS, WAIS and Greenland are shedding additional ice into oceans at a increasing rate. By the end of the 21st century with BAU practices on going we are lookng at 1 ft to 1 metre of average sea level rise. Its nice to know that Greenland might be more stable but it looks like WAIS is not as its not grouned on rock as much for example.

Elisabeth, #41, #42,
I think you make an excellent point taking thermal expansion during the Eemian into account.

Your assumption of Eemian global deep ocean warming of 3 C (wrt pre-industrial) may be a bit on the high side, although I could not find any evidence for or against that assumption. But logically speaking, if even Antarctica warmed significantly due to a higher of Arctic insolation during the Eemian, then warming (and thermal expansion) of the rest of the planetary oceans cannot be discarded.

It seems to me that if your numbers are anywhere close to actual ocean expansion during the Eemian, then having minor ice in Antarctica seems likely, or at least well within the uncertainty margins of the observations.

Pete,
While it is possible that sea level rise good increase to those rates, the current rate would only result in about 7 in. by 2100. Without a large contribution from either Greenland or Antarctica, those levels are a tad high. Eric’s work shows a more stable GIS, but the WAIS is only showing instability around Pine Island. Greater melt would need to occur in order to attain the higher levels you mention.

[Response: WAIS is showing instability *everywhere*. The Pine Island Glacier area is simply the area where the changes are largest, and where the most intensive in situ research has been done. Note by the way that there is no such place as “Pine Island”. That was the name of the ship, after which Pine Island Glacier and Pine Island Bay were named. –eric]

Eric,
I am aware of the conventional naming, and probably should have phrased my response differently. Instability in the WAIS is largely confined to the Amundsen coast. The Thwaites glacier showed both rapid advances and retreats over the past three decades, which is likely due to oceanic changes.

Those glaciers terminating in the Ross or Weddell sea are relatively stable. Granted, the ice shelves are a major player in their stability. Do you have any reason to suspect that these regions would exhibit changes similar to those in the Amundsen Sea?

[Response: I didn’t mean to imply lack of knowledge on your part; was just adding detail in case readers go confused. Yes, you are right of course — it’s mostly the Amundsen Coast — but it’s all of the Amundsen Coast. Thwaites and PIG have both fluctuated, and both have been forced by the ocean. Together, they drain about 20% of the ice sheet, so they alone matter. I agree with you about Ross and Filchner Ronne — they flow into cold water and I don’t think instability there is nearly as likely and certainly not detectable now. For a different view though, see Hellmer et al. (written up here, for example: http://www.rtcc.org/weddell-sea-region-in-west-antarctic-could-be-on-brink-of-change/>/a>

7 inches, thats not the projections stated in the IPCC FAR report and they did not take into account anything but thermal expansion of the oceans. I believe it has been commented on here in several good articles. 1 Meter is not that high a probability for ice melt is accelerating (or certainly has been) in recent decades.

“… beneath the West Antarctic Ice Sheet (WAIS) near the Weddell Sea. The location, shape and texture of the mile-deep basin suggest that this region of the ice sheet is at a greater risk of collapse than previously thought….
“… we could find no other region in West Antarctica more poised for change than this newly discovered basin at the head of the Filchner-Ronne Ice Shelf.”

OK Eric,
I think we are in agreement. Yes, others have speculated about what could occur, but this is largely guesswork at this time. By the time that we start seeing changes in these areas, it is likely that larger problems will have inundated us.

This is slightly off topic, so i ask the moderators to move the comment if it seems appropriate.

I have been thinking about PIG/Thwaites in the context of CDW and retrograde submarine/sub-ice bed. As i understand the Schoof treatment of the Weertman instability, the temperature of ice/water interface is at the pressure melting point, which increases with depth. But we see that the melt is driven under PIG/THW by (warming) CDW which is hotter. As the bed becomes deeper inland, the temperature difference between CDW and pressure melting point increases, ie the heat available to melt ice at the bed is larger, so to me this would exacerbate the already very strong instability. Is this incorporated into a more modern treatment ?

sidd

[Response: This is indeed true, and is incorporated into modern treatments. Some of the thermodynamic arguments you are raising are treated in a paper or three by Chris Little (let me know if you can’t find them), and are incorporated into a three dimensional-coupled-ocean-ice framework work by Olga Sergiekno. The latter is in review but I expect will be out some time in the next few months. –eric]

Looking at those deep images of the actual topography under the ice — the deep valleys with incised drainage channels all leading out toward the edges, and the smooth, broad fans of extruded glop around Antarctica — you can see the push the ice made shaped everything. Melting will reshape everything, no?

One thing that Box does not seem to pick up on is that Andy seems to think that 8 C of warming in unattainable. I think Andy may think that that is global warming rather than Greenland warming. But Greenland appears to have already warmed by about 3.5 C since the 1800’s http://www.nasa.gov/topics/earth/features/2012-temps.html so we could already be halfway to the conditions described in the new paper. Of course, the recent (2008-2012) warmth might be a spike but with Arctic amplification, an 8 C rise and greater is to be expected in the coming decades, contrary to Andy’s misconception.

Chris,
Jason Box (and co-authors) estimate that Greenland temperatures would only rise 2-4C by 2100, with a possibility of exceeding natural variability. They maintain that these temperatures have been reached previously in the past 4000 years.

Someone could disagree with the conclusion reached in the Kobashi, et. al. paper, that the current temperature is not due to natural variation, and they list several reason why. However, to claim that they have reached a similar conclusion is clearly contracted by the paper. Figure 1 clearly shows no anomaly, and their conclusion states, “The current decadal average surface temperature at the summit is as warm as in the 1930s-1940s, and there was another smiilarly warm period in the 1140s, indicating that the present decade is not outside the envelope of variability of the last 1000 years. Excluding the last millenium, there were 72 decades warmer than the present one”

Projections exceeding 2-4C where quoted from the IPCC AR4 report, not the Kobashi paper. Kobashi, et. al. stated, “a possibility of exceeding the upper bound (-28.7C) of the natural variabilty by 2100.” For reference, 2-4C above the 1970-1999 average is stated as -29.4 to -27.4C, such that -28.7C is clearly within that range. Taking bits and pieces of a report, and making preferential claims not support by the researchers should be discouraged.

“…. the conclusion reached in the Kobashi, et. al. paper, that the current temperature is not due to natural variation….” clearly tells us that your understanding of the paper is that the temperatures are NOT natural variation. Which of course is “clearly contracted” (sic – perfect typo) by your further ramblings. Nowhere does the study say as you do above, that “temperatures would only rise 2-4C by 2100″, in fact your later incomplete quote admits the paper states there is a definite possibility of temperatures exceeding 2-4C.

Yes, “Taking bits and pieces of a report, and making preferential claims not support(ed) by the researchers should be discouraged.”

flxible,
Forgive me for the confusing first statement. The paper clearly states that the current temperature is within natural variability. The paper states that there is a possibility of exceeding the upper bound of naturally variability (-28.7C), which is 2.7C above the reference period, and certainly within the 2-4C range. You are correct that the paper never states the possibility that temperatures will rise above 2-4C. There also exists the possibilty that temperatures will not rise above the two sigma level, and be constrainted below 2-4C above the reference. All this goes back to the statements that an 8C temperature rise in Greenland is unattainable.

“… the past variability of climate forcings can explain at least 10% of the multi-decadal to millennial variability in Greenland temperature over the past 4000 yr. An average temperature trend for the Northern Hemisphere (NH) over the past 4000 yr was also inferred from the ice-core derived Greenland temperatures. Lines of evidence indicate that the current decadal average temperature of NH is likely warmer than at any time over the past 4000 yr….”

“— Please Note —
Due to technical problems with the GISS webserver, parts of our site content are not available.
All interactive content, such as global temperature maps or station data plots using a web form, is currently disabled.”

So, a more detailed investigation is not possible at this time. But, since the baseline for the Nature paper is the pre-industrial millennium and the 1800’s data seem to be an OK substitute for that based on fig. 1 of the paper you cite, I don’t see a big issue. 7 C above that period seems well within reach. I’ve corrected the Nature paper estimate of 8 C for changing altitude also mentioned in the abstract.

82 flxible said, ” Nowhere does the study say as you do above, that “temperatures would only rise 2-4C by 2100″, in fact your later incomplete quote admits the paper states there is a definite possibility of temperatures exceeding 2-4C.”

And our Hero Dan H immediately replied, “Forgive me for the confusing…” You left out CONTINUOUS and YEARS AND YEARS, but hey, baby steps, eh?

Then Dan H courageously continues, “You are correct that the paper never states the possibility that temperatures will rise above 2-4C.”

#89–JimD, that’d be Iceland, not Greenland. There’s never been surface vulcanism observed in the latter, though there was a paper in 2007 suggesting that there could be a magma hotspot. (Somewhere in the Northwest I think.)

I asked a simple question. Please avoid attributing to others’ posts statements and sentiments they do not express. Such behavior is more befitting a troll like Dan.

Yurganov is the main researcher mapping satellite data of methane concentrations over the Arctic. These concentrations are at 600 millibars, quite high in the troposphere, iirc. I’ll see if I can get the link directly to his site, since I agree that AMEG sometimes is rather…selective in their use of otherwise legitimate data.

I am. That’s why I’m urging you to make more effort to explain.
This is the third or fourth time around, on this same issue.

When you post the AMEG/Yurganov pictures, please — give people the information you know about the source — the lab that actually does the work, and what they said about how it’s being used. We’ve been through that before.

You’re writing for an audience, and for new readers who will come later.

Now — the topic here is Greenland. What research is current that hasn’t been talked about yet? Spring is coming. What glaciers and areas of the icecap have been instrumented? Are we still using mostly aircraft flight since the satellite coverage isn’t good? Which countries are actively doing the research?

And who’s got fishing rights in the new inland sea, once Greenland melts out?

I do think it is past time that they adjust the scale so that everything over 1920 ppb is not bright red. Clearly things have now shifted, so we need to know how much of that bright red area is how far above 1920 ppb.

My original question about all this remains–how much would a regional eruption of methane like this effect Arctic temperatures? Will winds tend to keep these elevated concentrations in the far north for a while, or will they quickly disperse over the globe. At that height, are they on their way to the stratosphere? If so, what effect might that have on the northern ozone hole this spring?